Release agents used in adhesive items such as adhesive tapes are roughly divided into silicones and other organic compounds. The silicone-type release agents are characterized by having a very low peel strength, but have the defect that a moderate degree of peel strength is difficult to obtain, it is difficult to obtain close adhesion to a variety of substrates, and coatings of these release agents require baking at high temperatures. In many adhesive products, a moderate degree of peel strength is desired, and therefore, the organic compound-type release agents have gained widespread acceptance.
The release agents of the latter type commonly contain long-chain alkyl groups or long-chain fluorinated alkyl groups in the molecules as branches or side-chains, and, as the inventors believe, exhibit their respective characteristics depending upon the type of a polymeric main chain to which the long-chain alkyl groups are bonded, or upon the manner of bonding.
All of the conventional release agents have one or more defects, and have not proved to be entirely satisfactory. Among these defects are included the following.
(1) The synthesizing or manufacturing method is not simple. Since raw materials of unstable quality are used, the quality of the resulting release agent is not stable. The cost of production is also high.
(2) The release agents do not have good solubility in solvents which have low toxicity and are suitable for practical coating purposes.
(3) Since these release agents generally have a low softening point (mostly below 80.degree. C.), they are liable to dissolve in adhesive agents owing to time lapse, heating aging, etc. even after coating.
(4) Since these release agents generally have low adhesion to substrates, they migrate into adhesive agents with time. Or, in peeling, they separate from the substrates and migrate to the surface of the adhesive agent to reduce the tackiness of the adhesive surface.
(5) There is little room for modification of the basic formulation of a release agent, and the types of substrates with which the release agents are compatible are limited.